Muljajew Irina, Weber Christine, Nischang Ivo, Schubert Ulrich S
Laboratory of Organic and Macromolecular Chemistry (IOMC), Friedrich Schiller University Jena, Humboldtstr. 10, 07743 Jena, Germany.
Jena Center for Soft Matter (JCSM), Friedrich Schiller University Jena, Philosophenweg 7, 07743 Jena, Germany.
Materials (Basel). 2018 Mar 30;11(4):528. doi: 10.3390/ma11040528.
Depending on the degree of grafting (DG) and the side chain degree of polymerization (DP), graft copolymers may feature properties similar to statistical copolymers or to block copolymers. This issue is approached by studying aqueous solutions of PMMA--OEtOx graft copolymers comprising a hydrophobic poly(methyl methacrylate) (PMMA) backbone and hydrophilic oligo(2-ethyl-2-oxazoline) (OEtOx) side chains. The graft copolymers were synthesized via reversible addition-fragmentation chain transfer (RAFT) copolymerization of methyl methacrylate (MMA) and OEtOx-methacrylate macromonomers of varying DP. All aqueous solutions of PMMA--OEtOx (9% ≤ DG ≤ 34%; 5 ≤ side chain DP ≤ 24) revealed lower critical solution temperature behavior. The graft copolymer architecture significantly influenced the aggregation behavior, the conformation in aqueous solution and the coil to globule transition, as verified by means of turbidimetry, dynamic light scattering, nuclear magnetic resonance spectroscopy, and analytical ultracentrifugation. The aggregation behavior of graft copolymers with a side chain DP of 5 was significantly affected by small variations of the DG, occasionally forming mesoglobules above the cloud point temperature (T), which was around human body temperature. On the other hand, PMMA--OEtOx with elongated side chains assembled into well-defined structures below the T (apparent aggregation number (N = 10)) that were able to solubilize Disperse Orange 3. The thermoresponsive behavior of aqueous solutions thus resembled that of micelles comprising a poly(2-ethyl-2-oxazoline) (PEtOx) shell (T > 60 °C).
取决于接枝度（DG）和侧链聚合度（DP），接枝共聚物可能具有与无规共聚物或嵌段共聚物相似的性质。通过研究包含疏水聚（甲基丙烯酸甲酯）（PMMA）主链和亲水低聚（2-乙基-2-恶唑啉）（OEtOx）侧链的PMMA-OEtOx接枝共聚物的水溶液来探讨这个问题。接枝共聚物是通过甲基丙烯酸甲酯（MMA）和不同DP的甲基丙烯酸OEtOx大分子单体的可逆加成-断裂链转移（RAFT）共聚反应合成的。所有PMMA-OEtOx的水溶液（9%≤DG≤34%；5≤侧链DP≤24）都表现出较低临界溶液温度行为。通过比浊法、动态光散射、核磁共振光谱和分析超速离心法验证，接枝共聚物结构显著影响聚集行为、在水溶液中的构象以及从线团到球粒的转变。侧链DP为5的接枝共聚物的聚集行为受DG的微小变化显著影响，偶尔在接近人体温度的浊点温度（T）以上形成介球粒。另一方面，具有伸长侧链的PMMA-OEtOx在T以下（表观聚集数（N = 10））组装成明确的结构，能够溶解分散橙3。因此，水溶液的热响应行为类似于包含聚（2-乙基-2-恶唑啉）（PEtOx）壳的胶束（T > 60℃）的行为。
